In thermal power plants using a large amount of fossil fuel and the like, flue gas generated by burning the fossil fuel in a boiler contains CO2. Methods that enable to reduce and recover CO2 in the flue gas by bringing the flue gas containing CO2 into gas-liquid contact with an amine CO2 absorbent in a CO2 absorber and causing the CO2 absorbent to absorb the CO2, and methods that enable to store recovered CO2 without releasing the CO2 to the atmosphere have been intensively studied.
For example, a method by which a CO2 absorbent absorbs CO2 in flue gas in a CO2 absorber to reduce CO2 from the flue gas, then the CO2 absorbed by the CO2 absorbent is liberated in a regenerator to regenerate the CO2 absorbent, and the regenerated CO2 absorbent is circulated again to the CO2 absorber to be reused to reduce CO2 from the flue gas is employed (see Patent Literature 1, for example). In this method, the CO2 absorbent having absorbed CO2 is heated with vapor in the regenerator, thereby liberating the CO2, and accordingly high-purity CO2 is recovered.
CO2 gas accompanied by water vapor, which is released from a rich solution and a semi-lean solution in the regenerator, is emitted from the top of the regenerator, then the water vapor in the CO2 gas is condensed by a condenser, and water generated in the CO2 gas is separated by a separation drum. The CO2 gas from which the water vapor has been separated is compressed by a plurality of compressors with the pressure gradually increased, thereby being recovered as compressed CO2. After being compressed by the compressors, the CO2 gas is pressed into an oilfield to be used for enhanced oil recovery (EOR), accumulated in an aquifer as a measure against global warming, or used as a synthetic raw material of chemical products.
When the CO2 gas is compressed, cooled, and pressed into the oilfield to be used for oil recovery or the like, moisture remaining in the CO2 gas is condensed by the compression to become condensed water, and then COD components are resolved or the like, are subjected to effluent treatment, and then are discharged to outside.